When building roadways, for example, paving machines may be used to deposit significant amounts of paving material. Because paving material can be expensive, and because the quantities used can be so large, applying pavement with a thickness that deviates from a desired thickness can have costly consequences. If the pavement is applied in a mat that is too thick, the paving company may run out of material before the paving is complete and be forced to purchase additional material. If the mat is too thin, the pavement could perform poorly and contribute to premature failure requiring costly repairs.
Mat smoothness is another factor important to the performance of pavement. For example, if a paved roadway has a bumpy surface, increased forces will be applied to the raised bumps when the tires of vehicles drive over them. In addition to the poor ride quality experienced by passengers and cargo, the increased forces on the bumps can lead to premature failure of the pavement. Thus, providing a mat with proper and uniform thickness does not, by itself, necessarily make for pavement that performs well. For example, if the pavement is laid in a mat of uniform thickness, on top of an uneven subsurface, the mat smoothness will be poor as the mat will have the same unevenness as the subsurface.
In addition to thickness and smoothness, the density of pavement can play an important role in the performance of pavement. In order to produce pavement with uniform density, the pavement should be uniformly compacted. In order to uniformly compact pavement, its temperature should be consistent because pavement with higher temperatures will compact more than pavement with lower temperatures. Therefore, uniformity of pavement density is dependent on the uniformity of the pavement temperature as it is being applied to a surface.
Systems have been developed that attempt to control the output of paving machines. For example, U.S. Pat. No. 5,393,167 issued on Feb. 28, 1995 to Fujita et al. (the '167 patent), teaches a paving machine having height sensors along the side of the machine for measuring the height of the paving apparatus with respect to the pre-existing surface on which the pavement is being laid. However, the '167 patent does not measure the height of the sensors with respect to the actual mat that has been laid. Therefore, the '167 patent estimates or approximates mat thickness based on the measured height of the paving apparatus, rather than measurements of the mat itself. Also, the '167 patent does not monitor the smoothness of the mat. Further, the '167 patent does not monitor the temperature of the mat.
The disclosed control system relates to overcoming one or more of the problems set forth above.